a(1) = 2; a(n) is smallest prime > 2*a(n-1).

Terms

a(0) =2a(1) =5a(2) =11a(3) =23a(4) =47a(5) =97a(6) =197a(7) =397a(8) =797a(9) =1597a(10) =3203a(11) =6421a(12) =12853a(13) =25717a(14) =51437a(15) =102877a(16) =205759a(17) =411527a(18) =823117a(19) =1646237a(20) =3292489a(21) =6584983a(22) =13169977a(23) =26339969a(24) =52679969a(25) =105359939a(26) =210719881a(27) =421439783a(28) =842879579a(29) =1685759167